1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens which is suitable for use in a broadcasting television camera, a cinema camera, a video camera, a digital still camera, and a silver-halide film camera, for example.
2. Description of the Related Art
In recent years, a zoom lens having a large aperture ratio, a high zoom ratio, and high optical performance is required for an image pickup apparatus such as a television camera, a cinema camera, a film camera, or a video camera. In particular, in the television/cinema camera as a professional video photography system, image pickup devices having image sizes of a wide range from ½ inch (diagonal length: 8 mm) and ⅔ inches (diagonal length: 11 mm) to 35 mm (diagonal length: about 28 to 43.3 mm) have been introduced in the market. Mainstream image pickup devices such as a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) have a substantially even resolution over the entire image pickup range, and hence a zoom lens for use with such image pickup device is required to have a substantially even resolution from a center to a periphery of the screen.
Moreover, further increases in number of pixels for the image pickup devices have been advancing, such as 1,920×1,080 pixels (1080i) for HDTV and 4,096×2,160 pixels for 4K, and the demands for increased performance of the zoom lens have become ever stronger with the increases in resolution. For example, a CCD compatible with ⅔-inch HDTV has an image size of 9.6 mm×5.4 mm and a pixel size of 5 μm×5 μm.
Meanwhile, in professional video photography, it is desired to strictly set a photography range (angle of field), in particular. On the other hand, a lens generally has a problem in that the angle of field changes accompanying focus adjustment (hereinafter referred to as breathing). On a telephoto side, a depth of field is shallow and hence the remaining change in angle of field, if any, accompanying the focus adjustment is not conspicuous, but on a wide angle side, the depth of field is deep and hence it appears as if zooming is performed.
As zoom lenses having a large aperture ratio and a high zoom ratio, there have conventionally been proposed a wide variety of zoom lenses of a so-called floating focus type in which a lens unit located on an object side of a zoom lens unit performs the focus adjustment and a plurality of lens units move accompanying the focus adjustment.
For example, Japanese Patent Application Laid-Open No. H07-151966 discloses a zoom lens having an F-number at a wide angle end of about 1.7 to 1.9, an angle of field at the wide angle end of about 57 degrees to 63 degrees, an angle of field at a telephoto end of about 1.5 to 5 degrees, and a zoom ratio of about 13 to 44. A first lens unit includes a first sub lens unit having a negative refractive power, a second sub lens unit having a positive refractive power, and a third sub lens unit having the positive refractive power, and is configured so that, during focus adjustment from an object at infinity to an object at a short distance, both the second sub lens unit and the third sub lens unit move to the object side.
Moreover, Japanese Patent Application Laid-Open No. H09-258102 discloses a zoom lens having an F-number at the wide angle end of about 1.8, an angle of field at the wide angle end of about 90 to 102 degrees, an angle of field at the telephoto end of about 13 degrees, and a zoom ratio of about 8 to 10. The first lens unit includes a first sub lens unit having the negative refractive power, a second sub lens unit having the positive refractive power, and a third sub lens unit having the positive refractive power, and is configured so that, during focus adjustment from the object at infinity to the object at the short distance, the second sub lens unit moves to an image side and the third sub lens unit moves to the object side.
In general, in order to attain a zoom lens having a large aperture ratio and a high zoom ratio in which aberration variations are small and optical performance is high over an entire zoom range and an entire focus range, and in which the breathing is little at the wide angle end, there occurs a problem in that the number of lenses is increased, which leads to an increase in size of the entire lens system. Further, in order to attain a zoom lens having high optical performance in which the aberration variations are small over the entire focus range at the telephoto end, there occurs a problem in that the number of lenses of the first lens unit is further increased, which leads to an increase in size of the entire lens system. This tendency becomes more conspicuous as a focal length at the telephoto end becomes longer.
In order for the zoom lens to have a large aperture ratio (F-number of about 1.8 to 2.7), a wide angle of field, and a high zoom ratio (zoom ratio of 7 to 70) and to reduce the breathing at the wide angle end (to 4% or lower), the refractive powers, lens configurations, aberration contributions, and the like of the lens units need to be set appropriately. In particular, in order to suppress the breathing at the wide angle end and the aberration variations during focusing at the telephoto end at the same time while attaining reductions in size and weight of the entire zoom lens, settings and refractive power arrangements of the sub lens units which move for focusing of the first lens unit, configurations of sub systems, and the like need to be set appropriately.
When the focus type disclosed in Japanese Patent Application Laid-Open No. H07-151966 is used, it is difficult to suppress the breathing at the wide angle end. Further, with the refractive power arrangement and the lens configurations of Japanese Patent Application Laid-Open No. H09-258102, it is difficult to attain both the high optical performance and the suppression of the breathing at the wide angle end in the zoom lens having an angle of field at the telephoto end of less than 10 degrees.